The use of a cyclone, or multiple cyclones connected in parallel or series, is known to be advantageous in the separation of particulate matter from a fluid stream. Currently, many vacuum cleaners, which are sold for residential applications, utilize at least one cyclone as part of the air filtration mechanism.
U.S. Pat. No. 4,826,515 (Dyson) discloses a cyclonic vacuum cleaner having two cyclonic stages, namely a first stage for separating larger particulate matter from an air stream and a second stage for separating finer particulate matter from the same air stream. Each cyclonic stage comprised a single cyclone wherein separated particulate matter was collected in the bottom of the cyclones.
A difficulty experienced with cyclonic separators is the re-entrainment of the separated particulate matter back into the outgoing fluid flow. Deposited particles exposed to a high-speed cyclonic flow have a tendency to be re-entrained. One approach to resolve this issue is to use a plate positioned in a cyclone container to divide the cyclone container into an upper cyclone chamber, which is positioned above the plate, and a lower dirt collection chamber, which is positioned below the plate. See for example Conrad (U.S. Pat. No. 6,221,134). Accordingly, the portion of the cyclone casing below the plate functions as a dirt collection chamber wherein re-entrainment of separated particulate matter is impeded.